|Power Supply Voltage, VCC Pin, Continuous Voltage||−0.3 to 35V|
|Maximum Voltage on Low Power Pins CS, FB and Fault||−0.3 to 35V|
|Maximum Voltage on DRV Pin||−0.3 to 20V|
|High Voltage Pin||−0.3 to 650V|
|Maximum Junction Temperature||150°C|
|Storage Temperature Range||−60 to 150°C|
The NCP1239 is a fixed-frequency current-mode controller featuring a high-voltage start-up current source to provide a quick and lossless power-on sequence. This function greatly simplifies the design of the auxiliary supply and the VCC capacitor by activating the internal start-up current source to supply the controller during start-up, transients, latch, stand-by etc.
With a supply range up to 35 V, the controller hosts a jittered 65 or 100-kHz switching circuitry operated in peak current mode control. When the power on the secondary side starts to decrease, the controller automatically folds back its switching frequency down to minimum level of 26 kHz. As the power further goes down, the part enters skip cycle while limiting the peak current that insures excellent efficiency in light load condition.
NCP1239 features a timer-based fault detection circuitry that ensures a quasi-flat overload detection, independent of the input voltage.
The NCP1239 implements a standard current mode architecture where the switch-off event is dictated by the peak current setpoint. This component represents the ideal candidate where low part-count and cost effectiveness are the key parameters, particularly in low-cost ac-dc adapters, open-frame power supplies etc. The NCP1239 packs all the necessary components normally needed in today modern power supply designs, bringing several enhancements such as a non-dissipative over power protection (OPP), a brown-out protection or HV start-up current source.
Implementing peak current mode control operating at a 65 or 100-kHz switching frequency, the NCP1239 offers a fixed internal compensation ramp that can easily by summed up to the sensed current. The controller can be used in CCM applications with wide input voltage range thanks to its fixed ramp compensation that prevents the appearance of sub-harmonic oscillations
A portion of the bulk voltage is internally sensed via the high-voltage pin monitoring (pin 8). When the voltage on this pin is too low, the part stops pulsing. No re-start attempt is made until the controller senses that the voltage is back within its normal range. When the brown-out comparator senses the voltage is acceptable, de-latch occurs and the controller authorizes a re-start synchronized with VCC(on).
The high input voltage sensed on the HV pin is converted into a current. This current builds an offset superimposed on the current sense voltage which is proportional to the input voltage. By choosing the resistance value in series with the CS pin, the amount of compensation can be adjusted to the application.
Low standby power results cannot be obtained with the classical resistive start-up network. In this part, a high-voltage current-source provides the necessary current at start-up and turns off afterwards.
An internal low-frequency modulation signal varies the pace at which the oscillator frequency is modulated. This helps spreading out energy in conducted noise analysis. To improve the EMI signature at low power levels, the jittering will not be disabled in frequency foldback mode (light load conditions).
A continuous flow of pulses is not compatible with no-load/light-load standby power requirements. To excel in this domain, the controller observes the feedback pin and when it reaches a level of 1.9 V, the oscillator starts to reduce its switching frequency as the feedback level continues to decrease. When the feedback level reaches 1.5 V, the frequency hits its lower stop at 26 kHz. When the feedback pin goes further down and reaches 1.0 V, the peak current setpoint is internally frozen. Below this point, if the power continues to drop